Gas generator composition comprising a poly(vinyl lower alkyl ether) and oxalohydroxamic acid



chanical device.

United States Patent filice BJfib/lh Patented Jan. 19, 1965 GAS GENERATGR CGMEUSETIIUN (IGMPRISHNG A PQLYWINYT. LUWER ALKYL ETHER) AND 9X- ALOHYDLQSXAMIC ACE) John (I. Merges, 51, Wilmington, Deh, assignor to Thiohol Chemical Corporation, Bristol, PZL, a corporation of Delaware No Drawing. Filed Euly 1, 1963, der. N 292,099

8 Claims. ((31. 149-109) 1 The present invention relates to a novel composition of matter, and more particularly to a solid propellant composition of the type used in auxiliary power sources to generate gases under pressure at moderately low temperatures for operating a variety of pressure fluid actuated devices.

In the aeronautical industry, lightweight, gas generating auxiliary power sources are extensively used for a variety of operations, particularly those operations wherein a rather substantial amount of power of relatively short duration is required to actuate some me- For example, such gas generators are used as starters for jet engines, hydraulic pumps and alternators in electrical power systems, as well as starters for the large turbo-pump systems of liquid propellant rockets. They are also used as a power source for small reciprocating piston pumps for hydraulic systems. In some cases the generated gas is applied directly, under pressure, to a liquid to be moved, for example as in the pressurization of the fuel tanks of a liquid propellant rocket system.

. Gas generating compositions are similar, in some repositions should be insensitive to shock, homogeneous in content, have substantial elasticity to minimize voids and burn evenly and consistently. This latter property is suitably expressed in terms of a burning rate exponent (n) which should lie Within the range 0.20 to 0.40, a value as close to 0.30 as possible being preferred. The exponent (n) is part of the standard burning rate formula which is described on page 316 of Rocket Propulsion- Elements by G. P. Sutton, 2nd edition, 1956.

Usually, gas generating compositions are composed of an inorganic oxidizer and an organic binder. It is customary to use ammonium nitrate in gas generating compositions instead of a more energetic oxidizer such as ammonium pherchlorate to achieve greater stability in storage and low flame temperature during burning. Ammonium nitrate by itself will not support combustion without the addition of substantial amounts of oxygen.

, cent do not support combustion satisfactorily. Another tactor which contributes to uniform and smooth combus- Z tion is the maintenance of stoichiometric oxygen balance for the production of water, carbon monoxide and nitro gen during combustion. Therefore, binder material components capable of furnishing a part. of the oxygen for combustion of the grain are used to supply any oxygen deficiency in the composition. I

Generally, polyester resins are used as fuel binders in gas generating compositions. densing polyhydric alcohols with unsaturated polybasic acids to form unsaturated linear polyesters, The compound is then reacted with a compound having vinyllic unsaturation, such as styrene, in the'presence of a peroxide catalyst, to form a solid resin. In using this type of polyester, substantial amounts of a plasticizer are necessary in order to obtain the desired physical properties.

Another method involves the preparation of a carboxyl-terminated linear polyester that is cured through the carboxy groups. These resins are made by condens ing a polyhydric alcohol with a polycarboxylic acid to give a liquid carboxyl-terminated copolymer. Use of this polyester resin does not require a plasticizer.

However, use of polyester resins and ammonium nitrate ingas generating compositions has serious disadvantages. As tated hereinabove, ammonium nitrate cannot support combustion. Additional oxygen must be supplied to the system. Further, the polyesters must be cast and cured and do not adapt themselves readily to compaction into shaped charges. The amount of solids present in such a composition is limited to about percent because of processing difiiculties and the necessity of having an adequate supply of oxygen. Ammonium nitrate compositions also have high burning rate exponents (n). The exponents of such compositions are usually 0.6 or hgher. By definition, a composition having an exponent of 1.0 is an explosive, and the slightest shock causes detonation. It is therefore apparent that an exponent as low as possible is desired.

It is therefore an object of the present invention to provide a novel composition suitable for gas generators. It is a further object to provide a gas generating composition that can be molded into pressed charges.

It is an object to provide a gas generating composition that can be extruded. 1

It is also an object to provide a gas generating composition which permits higher oxidizer loadings than here tofore possible.

It is an object to provide a gas generating composition containing an organic oxidizer which is capable of selfsustaining combustion.

It is an object to provide a gas generating composition which burns smoothly and evenly, has a very low burning rate exponent (n), has a low flame temperature, and a noncorrosive and nonerosive exhaust gases.

Other objects will be apparent to those skilled in the art from a consideration of the following detailed description of the invention. I

It has now been found that a composition comprising normally form-stable poly(vinyl lower alky'l ether), par ticularly poly (vinyl ethyl ether) and a novel organic oxidizer is especially useful as gas generating compositions; The poly(vinyl lower alkyl ether) used in making the gas generating compositions of this invention can be either form-stable high molecular weight amorphous poly(vinyl They are formed by con- 1 sass les- 3 crystalline poly(vinyl lower alkyl ether) or a blend thereof. The characteristics and properties of these formstable (poly(.vinyl lower alkyl ethers) andv their manner of preparation is more fully described below.

The novel organic oxidizer used in the compositions of this invention is oxalohydroxamic acid of the following structural formula:

no-c=Non.

HO(B=NOH This compound, in its pure form, decomposes stoichiometrically at 335 F. to give carbon monoxide, water and'nitrogen. This material is self-sustaining after com.-

bustion and generates large volumes of gas rather slowly.

Use of oxalohydroxamic acid eliminates the need for large amounts of highly oxygenated binders. This, in turn, permits the ,formulation of a composition which can be readily extruded, compacted into a gas generator case or into shaped charges useful for a variety of applications.

with a suspension of hydroxylamine hydrochloride in an;

inert organic solvent such as pentane or hexane.

V (if a catalyst together with an activator, such as powdered solid carbon dioxide and/ or a chlorinated alkane such as chloroform. An induction period of about two hours is usually observed prior to commencement of the polymeri zation, which is generally complete in 2.5 to 3 hours.

The crystalline poly(vinyl lower'alkyl ether) prepared is stable in form and has an intrinsic viscosity in the range of 0.2 to 2.0 dm./g., a molecular weight of 10,000 to 700,000 and ;is crystalline to the extent of at least percent, with a range of to percent as determined by conventional X-ray ditfraction methods. The crystalline'polymer has a tensile strength of 1,000to 2,000 psi.

and an elongation of at least 400 percent.

Accordingto' the present invention, the amorphous hig molecular weight poly(vinyl lower alkyl ether) or the crystalline high molecular weight poly(vinyl lower alkyl ether) or mixtures thereof are intimately admixed or blended with the novel organic oxidizer of this invention,

oxalohydroxamic acid, to form the gas generator charges of this invention.

The polymer is suitably prepared as a solution in an The oxalohydroxamic acid is added and blending is continued until a substantially homogeneous mixture is obtained.

hydrous alcohol. Another method involves the treatment a of an alcoholic solution of hydroxylainine hydrochloride with gaseous ammonia.

The amorphous, normally form-stable poly (vinyl lower alkyl ether) which is suitably used in the compositions of the present invention can be prepared using a catalyst system comprising zinc chloride and t-butyl chloride with I the vinyl lower alkyl ether. The polymerization is conveniently conducted in bulk, using as a catalyst 0.2 to 10 parts by weight of t-butyl chloride per part'of zinc chloride. Inert solvents such as propane and the like, however, are also suitably used. It has been found convenient to conduct the polymerization with continuous stirring at about the boiling point of the mixture. Polym erization for about 1 to 48 hours produces poly(vinyl lower alkyl ethers) which have high molecular weights of 40,000 and above.

Amorphous poly(vinyl lower alkyl ethers) suitable for making the compositions of this invention are also conveniently prepared by polymerizing a vinyl lower alkyl ether monomer in the presence of a catalyst prepared by combining 1 to 500 parts by volume of a hydrogen containing chloromethane, such as chloroform, with one part by volume of a boron trifiuoride-diethyl ether. Only about 1.5 parts by weight of this catalyst complex per 100 parts by weight of monomer'are required and polymerization is generally complete in two hours.

In addition, form-stable amorphous poly(vinyl lower alkyl ethers) suitable for use in the compositions of this invention are suitably formed by polymerizing a vinyl lower alkyl ether in the presence of a boron trifluoride ether catalyst at very low temperatures, about 90 to .-115 F. A hydrocarbon solvent such as propane is advantageously employed and polymerization times of about /2. to 24 hours are used.

,The amorphous, form-stable poly(viny1 lower alkyl ether) described above has an intrinsic viscosity of about 0.2 to 1.3 dl./ g. The material is resilient and undergoes cold flow stretched. It also has a molecular weight of at least 10,000 and usually 40,000 to 330,000.

The crystalline poly(vinyl lower'alkyl ether) is conven iently prepared by polymerizing a vinyl lower alkyl ether in a hydrocarbon solvent such as propane at low/temperacharacteristics: I

Molecular weight 190,000 Tensile strength, p.s.i .Q. 993

Elongation, percent 4737 intrinsic viscosity, dl./gm. i 0.95

tures, about to -115 F. with a boron trifiuoride ether complex, such as boron trifluoride-diethyl ether, as

Tins operation is conveniently carried out in a vertical planetary mixer. The solvet is removed by conventional means and the homogeneous blend is pressed into a suitable mold for subsequent use. The blend can also be extruded. Alternatively, the .oxalohydroxamic acid and the pol (vinyl lower alkyl ether) are tumbled in a ball, mill until thorou hly mixed. This can be'accomplished with the components either in solution or as solids.

The novel compositions of this-invention, in addi ion to their utility as gas generators, find use as aerosols for dispersing dyes and other reagents. Further, known cooling agents such as oxalic acid and oxamide can be incorporated into the compositions to give a wide variation in flame temperature. 7

. Example 1 A reaction rnixture is formed from 19 parts by weight of propane, 37.5 parts of vinyl methyl ether, 60 parts of powdered solid carbon dioxide and 0.6 part of boron trifiuoride-ethyl ether.- The mixture is made in a vessel cooled by a surrounding mass of solid carbon dioxide and provided with a solid carbon dioxide condenser and is prepared by adding allot the componentsinthe order specified, with the mixture of propaneand vinyl methyl et'rer being cooled to ll0 F. prior tothe addition of the other components. The resultant mixture was then allowed to stand at -110 for 2% hours a the end of which time polymerization has taken place. The polymerization mass is then quenched with methanol saturated with ammonia gas containing 1 percent thymol, the quenching mixture being used in the quantity of 0.2

volume per volume of polymerization mass, There is then added 1 volume of methanol and the mixture is stirred to dissolve the polymer. After separation of the solvent, the polymer is dried to constant 'weight in an oven at F. i

There are thus recovered from the reaction mass 36 parts of crystalline polymer, representing a yield of 96 ercent, and the polymer is found to have the following 'Example 2 A catalyst is prepared by combining 1 part by volume of boron trifiuo-ride-ether complex with 50 par-ts of chloro- 133 parts of vinyl methyl ether there is added l part of the above-described catalyst. The flask is provided with a solid carbon dioxide condenser and with a thermometer and prior to addition of the catalyst it is packed in wet ice. After addition of the catalyst, reaction begins with rapid reflux from the condenser. After about only three minutes, the reaction becomes relatively quiet, leaving a colorless liquid. This liquid continues to thicken as the reaction proceeds and after about two hours the reaction mixture isquenched and the polymer recovered as described 'in Example-1.

There is thus recovered from the reaction mixture in 75 percent yield a clear, colorless, non-tacky polyvinyl methyl ether having an intrinsic viscosity (dL/gm.) of 0.8 and a molecular weight of 150,000.

Example 3 In a flask provided with a water condenserthere are mixed 317 parts by volume of pentane, 130 parts by volume of vinyl ethyl ether and 0.8 part by volume of the boron trifluoride-ethyl ether-chloroform catalyst described in Example 2, the catalyst being added in two 0.4 part increments spaced 15 minutes apart. After addition of the second'increment, reaction becomes apparent as the temperature rises from room temperature to 95 F. After 4 hours the polymerization mixture is quenched and the polymer recovered in the manner described in Example 1, except that the quenching mixture comprises equal parts of pentane and ammonia. The poly(vinyl ethyl ether) thus recovered is clear and colorless with an intrinsic viscosity (dl./ gm.) of 0.39.

Example 4 Substitution of an equimolar amount of vinyl ethyl ether for the vinyl methyl ether in Example 1 yields crystalline poly(vinyl ethyl ether) with a molecular weight of 200,000. The intrinsic viscosity is 0.45 dl./gm.

Example 5 'Eighty parts of metallic sodium is dissolved in 1600 parts of ethanol, and the resulting solution is added to a solution of 240 parts of hydroxylamine hydrochloride in 1600 parts of methanol. The resulting sodium chloride is filtered off and 169.4 parts of diethyl oxalate is added slowly to the filtrate with stirring. Precipitation occurs after a short time and the reaction mass is permitted to stand overnight. The alcohols are filtered off and the solid material is covered with glacial acetic acid. After the addition of several parts of water, the suspension is heated on the steam bath for 3 to 4 hours. The solid product is removed by filtration and is recrystallized from water at 176 F. to give oxalohydroxamic acid melting at 335 F. (doe).

Example 6 The amorphous poly(vinyl ethyl ether) prepared in Example 3 is prepared in a 25 percent solution in hexane. The solution is further diluted to five percent with pentane. A suflicient volume equivalent to three parts by weight of polymer is stirred with 97 parts by weight of oxalohydroxamic acid in a vertical planetary mixer, making sure all surfaces of the oxidizer are wet. This takes approximately ten minutes. The solution is then evaporated to dryness at room temperature in one hour with stirring. A stream of air directed across the mixture during stirring greatly facilitates the evaporation. The mixture is placed in a suitable mold and subjected to pressures of 6000 p.s.i. This composition burns smoothly leaving no residue. Av burning rate exponent of 0.3 is

obtained and a flame temperature of 1900 F. is measured.

The amount of polymer present in the composition is varied by suitable changes in the amount of polymer solution used. Alternatively, the polymer solution and oxidiz er can be placed in a ball mill and tumbled for several by raising the temperature and applying a vacuum.

Example 7 A mixture of 50 percent amorphous poly(vinyl ethyl ether) and 50 percent crystalline poly(vinyl methyl ether) prepared in Example 1 is prepared in 25 percent solution with hexane. The solution is further diluted to five per- .cent with pentane. A suflicient volume equivalent to five parts by weight of polymer is stirred with 4.8 parts by weight of oxalohydroxamic acid and 47 parts by weight of oxalic acid in a vertical planetary mixer. The procedure described in Example 6 is followed, except that 20,000 p.s.i. pressure is used for compaction. A burning rate exponent of 0.25 is obtained and a flame temperature of 700 F. is measured.

Example 8 Substitution of 30 parts of oxamide for 30 parts of the oxalohydroxamic acid in Example 5 and otherwise following the procedure described therein, wields a gas generator composition having a flame temperature of 1000 F. and a burning rate exponent of 0.33.

In order to obtain optimum combustion, particle sizes as small as possible are desired. It has been found that a particle size of three to microns gives superior results and the solids used herein are reduced as necessary in a suitable apparatus, such as a hammer mill.

Results similar to those described above are also achieved by using other amorphous poly(vinyl lower alkyl ethers) such as the methyl or propyl derivative or mixtures thereof. Further, mixtures of the amorphous or crystalline poly(vinyl lower alkyl ethers) can also be used. Five parts by weight or less of polymer are sufficient to obtain the desired results.

The oxidizers can be admixed with up to 50 percent of a coolant such as oxalic acid, oxamide or ammonium oxalate to give even lower flame temperatures. The flame temperature can be varied in the range 750 to 2100 F. by control of the amount of coolant added. Compaction can be accomplished with pressures in the range of 1,000 to 100,000 p.s.i V

The mixture of polymer and oxidizer can be compacted directly into a gas generator engine or a suitable mold. If the compacting is done directly into the engine, the engine case is suitably lined with a solution coating of the same polymer used in the gas generator composition. Further, if the compressed charges are removed from the mold and burned in the open air, they act as aerosols and disperse material over a wide area. It has been found that 50 percent by weight of various dyes or chemical agents such as l-methylaminoanthroquinone can be incorporated without any loss of combustion eflicicncy. During combustion, these agents are dispersed over a wide area. Thus, the compositions of this invention are useful vehicles for the dispersion of such agents in addition to being superior gas generator compositions. Also, other additives such as combustible metal powders such as magnesium and aluminum and other burning rate control agents such as ferric oxide can be added to alter or control combustion characteristics as desired. Such procedures are well known to those skilled in the art.

This composition can also be extruded as well as cornpacted. The extrusion can be accomplished by standard methods in either rod or ribbon form. The extrusion apparatus is conveniently coated with an aliphatic hydrocarbon, such as pentane, to prevent sticking. The ribbons or rods are allowed to dry for about 30 minutes, and then are packed into the engine case. i

, It will be obvious to those skilled in the art that many modifications both of materials and methods may be practiced without departing from'the invention. The foregoing description is illustrative only and should not be construed as limiting the invention eitherin spirit or in scope. r

'2' What is claimed is: 1. A gas generating composition comprising essentially a poly(vinyl lower alkyl ether) and oxalohydroxamic acid. 7

2. A composition defined as in'claim .1 comprising a major amount of oxalohydroxamic acid and a minor amount of a poly(vinyl lower alkyl ether).

3. A composition defined asin claim 2,-wherein the poly (Vinyl lower alkyl ether) is poly(vinyl methyl ether). 4. A composition defined as inclaim 2, wherein the poly(vinyl lower alkyl ether) is an amorphous poly(vinyl lower alkyl ether).

5. A composition defined as in claim 2, wherein the 7.'A compositiondefined as in claim 2, wherein the poly(vinyllower alkyl ether) is amorphous poly(vinylethyl ether).

8. A composition defined as in clairn 2, whereinthe poly(vinyl lower alkyl ether) is crystalline poly(vinyl ethyl ether).

No references cited. 

1. A GAS GENERATING COMPOSITION COMPRISING ESSENTIALLY A POLY(VINYL LOWER ALKYL ETHER) AND OXALOHYDROXAMIC ACID. 